This invention relates generally to non-linear amplifiers and, more particularly, to logarithmic amplifiers employing a single amplifier stage with positive non-linear feedback. Logarithmic amplifiers are often used in applications where there is a need to compress an input of large dynamic range into an output of small dynamic range. One means for providing the logarithmic relationship is to use a logarithmic detector, constructed from a properly biased diode matrix, and driven by a linear amplifier. Another technique is to design an amplifier that has high gain at low input levels and low gain at high input levels, thus producing a logarithmic input-output relationship.
One example of a logarithmic amplifier with a high gain at low input levels and low gain at high input levels can be found in U.S. Pat. No. 3,646,456, issued to Kauffman et al., and assigned to the assignee of the present invention. Kauffman employs a plurality of non-linear amplifier stages connected in cascade. The gain of each stage is initially greater than unity and is reduced to unity upon switching of an input limiter to a high-impedance state when the input signal exceeds a predetermined amplitude.